From: Al Viro <viro@zeniv.linux.org.uk>
To: David Laight <David.Laight@aculab.com>
Cc: "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
gus Gusenleitner Klaus <gus@keba.com>,
Al Viro <viro@ftp.linux.org.uk>,
Thomas Gleixner <tglx@linutronix.de>,
lkml <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@redhat.com>, "bp@alien8.de" <bp@alien8.de>,
"dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
"x86@kernel.org" <x86@kernel.org>,
"David S. Miller" <davem@davemloft.net>,
"dsahern@kernel.org" <dsahern@kernel.org>,
"kuba@kernel.org" <kuba@kernel.org>,
Paolo Abeni <pabeni@redhat.com>,
Eric Dumazet <edumazet@google.com>
Subject: Re: [RFC][PATCHES v2] checksum stuff
Date: Fri, 8 Dec 2023 18:35:09 +0000 [thread overview]
Message-ID: <20231208183509.GC1674809@ZenIV> (raw)
In-Reply-To: <ce18effbe40c47bfb48f87e7ee4f8141@AcuMS.aculab.com>
On Fri, Dec 08, 2023 at 03:56:27PM +0000, David Laight wrote:
> > You add them as natural numbers. If there is no carry and result
> > fits into N bits, that's it. If there is carry, you add it to
> > the lower N bits of sum.
> >
> > Discussion of properties of that operation is present e.g. in
> > RFC1071, titled "Computing the Internet Checksum".
> >
> > May I politely suggest that some basic understanding of the
> > arithmetics involved might be useful for this discussion?
>
> Well 0x0000 is +0 and 0xffff is -0, mathematically they are (mostly)
> equal.
As representations of signed integers they are. However, the origin
of operation in question is irrelevant. Again, read the fucking RFC.
> I bet that ICMP response (with id == 0 and seq == 0) is the only
> place it is possible to get an ip-checksum of a zero buffer.
> So it will be pretty moot for copy+checksum with can return 0xffff
> (or lots of other values) for an all-zero buffer.
Egads... Your bets are your business; you *still* have not bothered
to look at the callers of these primitives. Given the accuracy of
your guesses so far, pardon me for treating any "I bet"/"it stands for
reason"/etc. coming from you as empty handwaving.
> In terms of copy+checksum returning an error, why not reduce the
> 32bit wcsum once (to 17 bits) and return -1 (or ~0u) on error?
> Much simpler than your patch and it won't have the lurking problem
> of the result being assigned to a 32bit variable.
In case you have somehow missed it, quite a few of the affected places
are in assembler. The same would apply to added code that would do
this reduction. Which is going to be considerably less trivial than
the changes done in that patch.
next prev parent reply other threads:[~2023-12-08 18:35 UTC|newest]
Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-18 6:18 [PATCH] amd64: Fix csum_partial_copy_generic() gus Gusenleitner Klaus
2023-10-18 7:36 ` Eric Dumazet
2023-10-18 15:12 ` Thomas Gleixner
2023-10-18 15:42 ` Al Viro
2023-10-18 17:37 ` Thomas Gleixner
2023-10-19 4:44 ` AW: " gus Gusenleitner Klaus
2023-10-19 5:02 ` Al Viro
2023-10-19 6:14 ` Al Viro
2023-10-19 6:39 ` Al Viro
2023-10-19 7:39 ` Eric Dumazet
2023-10-19 8:06 ` Al Viro
2023-10-20 8:32 ` Vincent Whitchurch
2023-10-20 20:27 ` David Laight
2023-10-21 7:15 ` Al Viro
2023-10-21 22:22 ` Al Viro
2023-10-22 11:03 ` David Laight
2023-10-22 11:11 ` Al Viro
2023-10-23 8:16 ` David Laight
2023-10-24 2:59 ` Al Viro
2023-10-22 19:40 ` [RFC][PATCH] fix csum_and_copy_..._user() idiocy. " Al Viro
2023-10-22 19:46 ` Al Viro
2023-10-23 10:37 ` Thomas Gleixner
2023-10-24 4:26 ` Al Viro
2023-10-24 12:31 ` Thomas Gleixner
2023-10-23 14:44 ` David Laight
2023-10-24 3:53 ` Al Viro
2023-12-05 2:21 ` [RFC][PATCHES v2] checksum stuff Al Viro
2023-12-05 2:23 ` [PATCH v2 01/18] make net/checksum.h self-contained Al Viro
2023-12-05 2:23 ` [PATCH v2 1/9] reiserfs: Avoid touching renamed directory if parent does not change Al Viro
2023-12-05 2:23 ` [PATCH v2 02/18] get rid of asm/checksum.h includes outside of include/net/checksum.h and arch Al Viro
2023-12-05 2:23 ` [PATCH v2 2/9] ocfs2: Avoid touching renamed directory if parent does not change Al Viro
2023-12-05 2:23 ` [PATCH v2 03/18] make net/checksum.h the sole user of asm/checksum.h Al Viro
2023-12-05 2:23 ` [PATCH v2 3/9] udf_rename(): only access the child content on cross-directory rename Al Viro
2023-12-05 2:23 ` [PATCH v2 4/9] ext2: Avoid reading renamed directory if parent does not change Al Viro
2023-12-05 2:23 ` [PATCH v2 04/18] Fix the csum_and_copy_..._user() idiocy Al Viro
2023-12-05 2:24 ` [PATCH v2 05/18] bits missing from csum_and_copy_{from,to}_user() unexporting Al Viro
2023-12-05 2:24 ` [PATCH v2 5/9] ext4: don't access the source subdirectory content on same-directory rename Al Viro
2023-12-05 2:24 ` [PATCH v2 06/18] consolidate csum_tcpudp_magic(), take default variant into net/checksum.h Al Viro
2023-12-05 2:24 ` [PATCH v2 6/9] f2fs: Avoid reading renamed directory if parent does not change Al Viro
2023-12-05 2:24 ` [PATCH v2 07/18] consolidate default ip_compute_csum() Al Viro
2023-12-05 2:24 ` [PATCH v2 7/9] rename(): fix the locking of subdirectories Al Viro
2023-12-05 2:24 ` [PATCH v2 08/18] alpha: pull asm-generic/checksum.h Al Viro
2023-12-05 2:24 ` [PATCH v2 8/9] kill lock_two_inodes() Al Viro
2023-12-05 2:24 ` [PATCH v2 09/18] mips: pull include of asm-generic/checksum.h out of #if Al Viro
2023-12-05 2:24 ` [PATCH v2 9/9] rename(): avoid a deadlock in the case of parents having no common ancestor Al Viro
2023-12-05 2:24 ` [PATCH v2 10/18] nios2: pull asm-generic/checksum.h Al Viro
2023-12-05 2:24 ` [PATCH v2 11/18] x86: merge csum_fold() for 32bit and 64bit Al Viro
2023-12-05 2:24 ` [PATCH v2 12/18] x86: merge ip_fast_csum() " Al Viro
2023-12-05 2:24 ` [PATCH v2 13/18] x86: merge csum_tcpudp_nofold() " Al Viro
2023-12-05 2:24 ` [PATCH v2 14/18] amd64: saner handling of odd address in csum_partial() Al Viro
2023-12-05 2:24 ` [PATCH v2 15/18] x86: optimized csum_add() is the same for 32bit and 64bit Al Viro
2023-12-05 2:24 ` [PATCH v2 16/18] x86: lift the extern for csum_partial() into checksum.h Al Viro
2023-12-05 2:24 ` [PATCH v2 17/18] x86_64: move csum_ipv6_magic() from csum-wrappers_64.c to csum-partial_64.c Al Viro
2023-12-05 2:24 ` [PATCH v2 18/18] uml/x86: use normal x86 checksum.h Al Viro
2024-01-03 22:02 ` Richard Weinberger
2023-12-05 2:27 ` [RFC][PATCHES v2] checksum stuff Al Viro
2023-12-06 11:10 ` David Laight
2023-12-06 22:43 ` Al Viro
2023-12-07 9:58 ` David Laight
2023-12-08 12:04 ` David Laight
2023-12-08 14:17 ` Al Viro
2023-12-08 15:29 ` Al Viro
2023-12-08 15:56 ` David Laight
2023-12-08 18:35 ` Al Viro [this message]
2023-10-19 11:45 ` AW: [PATCH] amd64: Fix csum_partial_copy_generic() Thomas Gleixner
2023-10-19 10:33 ` David Laight
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